While there have been improvements in detection, treatment and prevention techniques, dental caries remains a prevalent condition affecting people of all age groups. If not properly and promptly treated, caries could lead to permanent tooth damage and even to loss of teeth. Thus dental imaging based on an intra-oral camera is of great interest.
There exist known intra-oral cameras, such as those available from ACTEON Inc. of Mount Laurel, N.J., USA. Generally, intra-oral cameras are operated over a large working distance range that typically varies between about 1 mm to about 50 mm. They must also have a sizable depth of field (DOF), which is different at different working distances. Thus, focus adjustment is necessary to guarantee a good image quality. However, for most of the known intra-oral cameras including the one disclosed in U.S. Pat. No. 6,019,721 (Holmes et al.), focus adjustment is performed manually by operator adjustment to the distance between a lens and an imaging sensor. Conventional cameras do not have auto-focusing capability and must be separately adjusted for each image. Therefore they are not convenient in use.
There also exist known auto-focus cameras, such as those disclosed in U.S. Patent Application Publication No. US2008/0079897 (Goldfain et al.), U.S. Pat. No. 6,806,988 (Onuki et al.), and U.S. Pat. No. 7,236,696 (Higuma et al.). These earlier cameras, although relatively thin from front to back, are much too wide for intra-oral imaging applications. Their function of auto-focusing is usually achieved by adjusting the focal point of an optical lens relative to a fixed sensor. This may be done by moving the lens or lens assembly or, with a liquid lens, by changing its shape. Conventional cameras with auto-focus capability, although suitable for their intended uses in general imaging applications, cannot be easily used to image an intra-oral target due to their overall width.
While conventional auto-focusing cameras may have achieved certain degrees of success in their particular applications, they fail to meet the dimensional and operational requirements of intra-oral imaging. There is a need for an auto-focus intra-oral camera that is small in width, convenient in use, and capable of capturing images at high precision and at high speed.